Study On Model Parameters Identification Of Time-varying Structures Based On FBG Sensors

With the development of aerospace applications,time-invariant assumption is hard to meet the requirements of engineering analysis and design.It is inceasingly important to consider the time-varying characteristics of engineering structures.In addition,it is becoming much harder for the traditional methods of structural dynamics measurement mainly based on piezoelectric acceleration sensors to meet the needs of real-time structural health monitoring and on-line identification of modal parameters of spacecraft structures.Compared with the traditional acceleration sensors,fiber Bragg grating sensors have the advantages of small size,light weight,multiplexing,immunity to electromagnetic interference and so on,which make them well adapted to the on-line measurement and monitoring of spacecraft structures.This thesis studies on the method of structural dynamics experiment and modal parameter identification of time-varying structure based on fiber Bragg grating sensors.The main work of this thesis is as follows.(1)Research and application status of fiber Bragg grating sensors,strain modal analysis,modal parameter estimation methods of time-varying structures is summarized to supply the primary support for the further research on model parameters identification of time-varying structures based on fiber Bragg grating sensors.(2)The basic concept of strain mode is derived from displacement mode.The modal of strain mode is deduced.The orthogonality between strain modal shapes,the strain frequency response function and its characteristics are discussed.Those contests provide a theoretical basis for modal parameter identification and experimental verification of timevarying structures based on strain response.(3)A method for modal parameter estimation of time-varying systems based on support vector machines(SVM)is proposed and verified by a numerical example.Based on support vector machines(SVM),the parametric time-dependent autoregressive model is adopted to obtain the mathematical model of the modal parameter identification based on support vector machines(SVM).Finally a numerical example is adopted to verify the identification method.(4)The working principle and the basic technology index of the fiber Bragg grating sensor as well as the fiber Bragg grating sensing technology are introduced.Then the design parameters of the experimental parts are determined by pre-experimental analysis based on finite element model and the time-varying liquid-filled cylinder experiment system based on fiber Bragg grating sensers is designed and realized.(5)The experimental data of time-varying experiment and reference experiments are obtained by time-varying liquid-filled cylinder experiments and characteristic-freezing reference experiments.Firstly the results of the reference experiments are obtained.Then the experimental data of time-varying experiment are identified with functional series vector time-dependent autoregressive moving average(FS-VTARMA)model as well as support vector machines time-dependent autoregressive(SVM-TAR)model and functional series time-dependent autoregressive(FS-TAR)model based on single reference.By comparing the results of the reference experiments and time-varying experiment,the method of timevarying structures model parameters identification based on fiber Bragg grating sensors is verified.